The heart of a positron emission tomography camera (PET) is a set of gamma-ray detector rings surrounding the patient, such as disclosed in my U.S. Pat. No. 4,733,083. The detector rings consist of thousands of small scintillator detectors (crystals) closely packed together to form a ring without gaps in between. The scintillation light generated by the detector crystal on the detection of a gamma-ray is converted into electrical signal by a photomultiplier tube (PMT) optically coupled to each crystal. The highest image resolution achievable by any camera is equal to half the width of the scintillation crystal used in that camera. The crystal can be made very narrow (e.g. 1 mm), but the smallest available PMT is very big (10 mm). Hence, with the conventional crystal/PMT coupling, the best practically achievable image resolution for PET has been about 5 mm. In addition, with smaller detectors, the required number of crystal/PMT increases. The miniature PMTs are very expensive ($250 ea), and a typical high resolution PET requires 1500-2000 crystal/PMT channels. Hence the PMTs alone cost $500,000 plus additional affiliated signal processing electronics such as an amplifier per PMT, which is why PETs are expensive. Furthermore, the current commercial PETs, with their wider crystals, sample too coarsely in space that all the detectors are required to have a continuous scanning motion to improve the spatial data sampling. Moving 0.6-1.0 tons of the delicate detector system and keeping track of the instantaneous positions of all the detectors while each gamma-ray is being detected, is very costly mechanically and electronically.
The present invention aims to solve the three problems above:
(1) improving the ultimate PET image resolution with very narrow crystals without being restricted by the large size of the PMTs, so that image resolution of 2-3 mm can be achieved as compared to best current commercial camera resolution of 4.5-5 mm. PA1 (2) decrease the number of PMTs and their affiliated electronics to 25% of the conventionally required number to greatly reduce the component cost. PA1 (3) obviate the camera scanning motion by using very small detectors to improve the coarse spatial sampling problem to reduce the complexity and cost of the camera.